Add usage notice in readme file

[brettaufheber]

No description provided.

[pathob]

Good start, but my main concern still exists: A cache should clean up old entries at some point and it's not documented whether or how that works.

[brettaufheber]

@pathob
I added a notice in the readme that there is currently no cleanup mechanism implemented.

For this purpose i created a an issue: #11

[gebae]

In principle it is ok for me, but:

• A hint in the readme, how the cache entry hash is calculated, could be helpful for the users.
• It is not 100% clear, if the "parameters for all artifact types" can be used together with the resolve-using-config task. If yes, it would mean that the documentation of the cache-dir parameter for the resolve-using-config task is redundant.
• It is also not clear, if the cache-dir parameter can be part of the JSON config file (why not, actually?).

[brettaufheber]

Hello @gebae,
thank you for your review.
I will improve the readme file according to your suggestions.